1. Field of the Invention
The present invention relates to a relay device, a wireless communication system and a multicast relay method that realize multicast communications efficient and effective in mobile communications.
2. Description of the Related Art
WiMAX (Worldwide Interoperability for Microwave Access) is defined as a fixed wireless communication technology based on IEEE802.16. Standardization of the WiMAX technology for providing a fast wireless communication service is in progress. The WiMAX Forum® is an industry-led organization established as an organization for promoting the WiMAX technology. Non-Patent document 1 given below is a document issued by the WiMAX Forum® as a technical overview about the WiMAX technology.
Non-Patent document 1 describes a purport of supporting a multi BS (Base Station)-MBS (Multicast Broadcast Service) in the WiMAX technology. Specifically, the wireless communication system using the WiMAX technology is requested to provide, through multicast communications, a variety of contents such as a news program, a sports program, a weather forecast and traffic information.
IGMP (Internet Group Management Protocol) and MLD (Multicast Listener Discovery) are employed as multicast group management protocols in a way that participates in and leaves a multicast group in the multicast communications using an IP (Internet Protocol) protocol. The IGMP is the multicast group management protocol that supports IPv4, and the MLD is the multicast group management protocol that supports IPv6.
Patent document 1 given below discloses a method of efficiently transmitting multicast data in a LAN (Local Area Network) that supports the multicast communications. According to this method, when receiving a packet utilized on the multicast group management protocol, a table representing an associative relation between a host device and the multicast group is generated based on the received packet. Forwarding control is done with reference to this table so as to forward, when receiving a query packet, this query packet to all of ports other than a port to which the received packet is inputted in a plurality of ports. According to this method, the query packet can be surely forwarded to under a multicast router.
The Patent document 1 is “Japanese Patent Application Laid-Open Publication No. 2004-4251”.
The Non-Patent document 1 is “WiMAX Forum, “A Technical Overview and Performance Evaluation”, Mobile WiMAX-Part 1, Feb. 16, 2006”.
In real circumstances, however, none of the specific method for supporting the multi BS-MBS in the WiMAX technology is disclosed.
Especially in the wireless communication system using the WiMAX technology, the device provided with the multicast data is a mobile terminal, and hence, if the IGMP or the MLD is applied as it is, there might be a case where the multicast data can not be efficiently transmitted.